Sentinel-3 Delay-Doppler altimetry over Antarctica

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Abstract

The launch of Sentinel-3A in February 2016 represented the beginning of a new long-term series of operational satellite radar altimeters, which will provide Delay-Doppler altimetry measurements over ice sheets for decades to come. Given the potential benefits that these satellites can offer to a range of glaciological applications, it is important to establish their capacity to monitor ice sheet elevation and elevation change. Here, we present the first analysis of Sentinel-3 Delay-Doppler altimetry over the Antarctic ice sheet, and assess the accuracy and precision of retrievals of ice sheet elevation across a range of topographic regimes. Over the low-slope regions of the ice sheet interior, we find that the instrument achieves both an accuracy and a precision of the order of 10:cm, with ĝ1/498 :% of the data validated being within 50:cm of co-located airborne measurements. Across the steeper and more complex topography of the ice sheet margin, the accuracy decreases, although analysis at two coastal sites with densely surveyed airborne campaigns shows that ĝ1/460 :%-85:% of validated data are still within 1:m of co-located airborne elevation measurements. We then explore the utility of the Sentinel-3A Delay-Doppler altimeter for mapping ice sheet elevation change. We show that with only 2 years of available data, it is possible to resolve known signals of ice dynamic imbalance and to detect evidence of subglacial lake drainage activity. Our analysis demonstrates a new, long-term source of measurements of ice sheet elevation and elevation change, and the early potential of this operational system for monitoring ice sheet imbalance for decades to come.

Figures

  • Figure 1. a. Overview of the Lake Vostok (b), Dome C (c), Dronning Maud Land (d) and Wilkes Land (e) study sites. The background image in panel a is a surface DEM [Slater et al., 2017] overlaid upon the MODIS Mosaic of Antarctica (MOA) [Haran et al., 2006]. Panels b-e show the Sentinel-3 ground tracks (turquoise) at each study site, overlaid upon MOA.
  • Figure 2. Assessment of instrument precision at the Lake Vostok site in East Antarctica. a. The location of the two ground tracks crossing the center of the lake (Pass 138, cyan; Pass 260, magenta), plotted on a surface DEM [Slater et al., 2017], with other passes shown in white. For each pass, 14 cycles were accumulated between Dec. 2016 and Dec 2017. Panels b and d show the residuals from the mean elevation of all cycles. Panels c and e show the elevations along each pass (grey), together with the standard deviations of all measurements acquired at 400 m intervals (green bars).
  • Figure 3. Assessment of the accuracy of Sentinel-3A elevation measurements at the inland Lake Vostok (a-c) and Dome C (d-f) sites in East Antarctica. a,d. Elevation differences between Sentinel-3 and IceBridge. Sentinel-3 and IceBridge tracks are shown as thin white and turquoise tracks lines, respectively, and the background image is constructed from a CryoSat-2 DEM [Slater et al., 2017]. b,e. Distribution of Sentinel-3 – IceBridge elevation differences at the Lake Vostok (b) and Dome C (e) sites. c,f. Cumulative distribution of the absolute Sentinel-3 – IceBridge elevation differences at the Lake Vostok (c) and Dome C (f) sites.
  • Figure 4. Assessment of the accuracy of Sentinel-3A elevation measurements at the coastal Dronning Maud Land (a-c) and Wilkes Land (d-f) sites in East Antarctica. a,d. Elevation differences between Sentinel-3 and IceBridge. The background image is constructed from a CryoSat-2 DEM [Slater et al., 2017] and the colour scales differ for the two sites. b,e. Distribution of Sentinel-3 – IceBridge elevation differences at the Dronning Maud Land (b) and Wilkes Land (e) sites. c,f. Cumulative distribution of the absolute Sentinel-3 – IceBridge elevation differences at the Dronning Maud Land (c) and Wilkes Land (f) sites.
  • Figure 5. Comparison of 100 metre scale surface roughness at Dome C (a-d) and Lake Vostok (e-h). Panels a-c and e-g show profiles of elevation residuals acquired by the ATM airborne instrument at the locations marked by the red boxes in panels d and h, respectively. Residuals are computed by removing a quadratic trend from each elevation profile. In panels d and h, the airborne ground track is shown in turquoise, the bounds of the study area in white, and the background image is from the MODIS Mosaic of Antarctica (MOA) [Haran et al., 2006].
  • Figure 6. Rates of Antarctic surface elevation change derived from Sentinel-3A Delay-Doppler altimetry acquired between May 2016 and February 2018. The background image is a shaded relief derived from a DEM [Slater et al., 2017], overlaid upon the MODIS Mosaic of Antarctica (MOA) [Haran et al., 2006].
  • Table 1. Summary of Sentinel-3 orbit characteristics and the primary altimeter payload.
  • Table 2. Sentinel-3A validation statistics based upon comparison to IceBridge airborne altimetry at the four study sites.

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APA

McMillan, M., Muir, A., Shepherd, A., Escolà, R., Roca, M., Aublanc, J., … Benveniste, J. (2019). Sentinel-3 Delay-Doppler altimetry over Antarctica. Cryosphere, 13(2), 709–722. https://doi.org/10.5194/tc-13-709-2019

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